Variable Refrigerant Flow System with Decoupled Refrigerant and Air Distribution Subsystems

ABSTRACT

An indoor cassette unit for a variable refrigerant flow system. The cassette unit has a cabinet structure with a main housing. A heat exchanger, such as a refrigerant coil, and a motorized fan are retained by the cabinet structure. A primary air inlet is disposed in fluidic communication with an inner volume of the main housing, and a tapered duct section is interposed between the heat exchanger and the fan to establish a sub-volume within the main housing and a physically spaced distance between the heat exchanger and the fan. An inlet volume sensor and a volume control device can cooperate to act as an air inlet valve. A secondary housing with an inner volume can be fixed to the main housing. A filter rack is retained in juxtaposition with the heat exchanger. A return air inlet can be disposed in fluidic communication with the inner volume.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application No. 62/398,171, filed Sep. 22, 2016, which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to variable refrigerant flow air conditioning systems. More particularly, disclosed herein is a variable refrigerant flow air conditioning system wherein the refrigerant coil subsystem is decoupled from or disparately located in relation to the air distribution subsystem.

BACKGROUND OF THE INVENTION

Air conditioning is the process of achieving a more comfortable environment by altering the condition of the air, such as by one or more of heating, cooling, dehumidification or humidification, cleaning, ventilation, or air movement. In common usage, air conditioning, commonly referred to as AC or A/C, removes heat and humidity from air with the goal of distributing conditioned air within an occupied space to improve thermal comfort and indoor air quality. Air conditioning is often achieved through a refrigeration cycle, although evaporation and free cooling are also exploited. A complete system of heating, ventilation, and air conditioning is normally referred to as a heating, ventilation, and air conditioning or HVAC system.

Variable refrigerant flow or VRF is a HVAC technology of relatively recent origin. A VRF system uses refrigerant as the cooling and heating medium with the refrigerant being conditioned by an outdoor condensing unit and circulated within the building to multiple cassette fan-coil units or FCUs. The outdoor unit commonly includes one or more compressors and condensers while indoor cassettes typically include an expansion device, a heat exchanger, and a fan. The fan-coil units act as local air circulation units to circulate the indoor air. A coil within the unit is chilled or heated by the fluid, and the coil adjusts the temperature or humidity of the circulated air while the fan or blower circulates the indoor air. The VRF cassette fan-coil units, each with a coil and an air distribution device, are disposed within the occupied zone to deliver conditioned air. Cassettes can, for instance, be mounted on the wall or ceiling of the occupied zone to be heated or cooled.

VRF systems normally incorporate an inverter that converts incoming alternating current to direct current. The direct current passes through a frequency driver so that variable motor speed can be controlled. The variable motor speed enables variable refrigerant flow rather than simple on/off operation. Variable speed operation permits VRF systems to work only at the rate necessary, which allows for substantial energy savings at partial-load conditions. Embodiments of VRF systems are also known wherein multiple compressors of varying capacity are operated in response to changes in the cooling or heating requirements within the air conditioned space. Heat recovery VRF technology allows individual indoor units to heat or cool as required with resultant energy savings and greater control of the building's interior temperature.

Numerous VRF systems and improvements thereto have been disclosed by the prior art. For instance, U.S. Patent Application Publication No. 2017/0138619 of Sprayberry et al., which is incorporated herein by reference, is directed to what is characterized as an enclosed, modular multi-zone variable refrigerant flow air conditioning system. U.S. Patent Application Publication No. 2014/0208776 of Hu et al., which is also incorporated herein by reference, discloses a Multi-Split HVAC System with a first VRF outdoor unit. A first ducted variable speed indoor unit selectively exchanges refrigerant with first VRF outdoor unit, and a second indoor unit selectively exchanges refrigerant with the first VRF outdoor unit.

While such VRF HVAC systems offer benefits regarding energy savings and temperature control proximate to the cassettes, they suffer from a number of disadvantages. For instance, fan-coil units are poorly effective at distributing air. It is known, for example, that warm air is best distributed at the perimeter of a space, which is where the heat loss primarily occurs. Distributing warm air from the center of the room or in four different directions as is the case with current fan-coil cassette units is inefficient. Warm air, if being distributed from the ceiling, should be introduced into the space so that it can be sent vertically downward along the perimeter of the space. It is further recognized that cool air distributed from the wall may create drafts in the occupied zone.

VRF systems of the known prior art also exhibit disadvantages in relation to the need for ventilation air. Building codes normally require that commercial and institutional buildings with human occupants have fresh air supplied to the occupied zones. However, current VRF systems have no means or methods to accomplish such an introduction of fresh air. Consequently, independent fresh air systems are required to be installed.

Still another issue relating to current VRF systems relates to the temperature of the air being discharged from the fan-coil unit when in the heating mode within the occupied zone. To avoid excessive stratification and energy waste, ASHRAE recommends that discharge air temperature be no higher than fifteen degrees above the temperature of the respective zone. However, VRF systems often have discharge temperatures as high as 40 degrees above room temperature.

In view of the foregoing, it will be appreciated that there is a need for an improved variable refrigerant flow heating, ventilation, and air conditioning system that provides a solution to one or more of these known shortcomings of the systems of the prior art.

SUMMARY OF THE INVENTION

With an appreciation for the state of the art and the real needs summarized above, the present inventor set forth with the basic object of providing a variable refrigerant flow system that overcomes the disadvantages of prior systems while providing a plurality of advantages thereover.

A more particular object of the invention is to provide a variable refrigerant flow system capable of distributing air with increased effectiveness.

Another object of the invention is to provide a variable refrigerant flow system that is capable of permitting the introduction of fresh air thereby obviating the need for a separate fresh air system.

Still another object of the invention is to provide a variable refrigerant flow system wherein discharge air temperature can be within an improved range of air temperature within a conditioned zone.

In carrying forth one or more objects of the invention, an indoor cassette unit for a variable refrigerant flow system as taught herein can be considered to be founded on a cabinet structure comprising a main housing with an inner volume. A heat exchanger, such as a refrigerant coil, and a fan are retained by the cabinet structure. A motor is operative to drive the fan. A primary air inlet is disposed in fluidic communication with the inner volume of the main housing, and a duct section is interposed between the heat exchanger and the fan.

The duct section can be operative to establish a physically spaced distance between the heat exchanger and the fan and a substantially enclosed sub-volume within the main housing between the refrigerant coil and the fan. In certain practices of the invention, the duct section interposed between the heat exchanger and the fan can comprise a tapered duct section.

Further, an inlet volume sensing device and a volume control device can be operably associated with the primary air inlet to establish an inlet valve structure. In particular embodiments, the cabinet structure can have the main housing, and a secondary housing can be fixed to the main housing. The secondary housing has an inner volume. Embodiments of the indoor cassette unit are further contemplated wherein a filter rack is retained by the cabinet structure, such as in juxtaposition with the heat exchanger. Still further, indoor cassette units as disclosed herein can provide a return air inlet disposed in fluidic communication with the inner volume of the main housing.

The main housing can be considered to have a first end portion, a second end portion, and a mid-portion between the first and second end portions. The heat exchanger can then be retained in the first end portion of the main housing. Under practices of the invention, the primary air inlet can be retained in the second end portion of the main housing.

A return air inlet can additionally be disposed in the main housing. For instance, the return air inlet can be disposed in the second end portion of the main housing in parallel with the primary air inlet.

A discharge opening can be in fluidic communication with the inner volume of the main housing. For instance, where the primary air inlet is retained in the first end portion of the main housing, the discharge connection can be disposed in the second end portion of the main housing.

In other embodiments where the cabinet structure has a main housing and a secondary housing fixed to the main housing. The secondary housing has an inner volume. Under such constructions, the primary air inlet can be disposed in the secondary housing. A discharge connection can then be in fluidic communication with the main housing and the secondary housing.

A variable refrigerant flow system can be assembled exploiting one or more indoor cassette units as disclosed herein. Such a variable refrigerant flow system can have an outdoor condensing unit with at least one compressor, at least one condenser, a fan, and a variable speed motor. An inverter is operative to convert incoming alternating current to direct current supplied to the variable speed motor of the outdoor condensing unit. At least one indoor cassette unit is employed, and refrigerant lines connect the outdoor condensing unit and the at least one indoor cassette unit to establish a refrigerant loop.

The at least one indoor cassette unit has a cabinet structure comprising a main housing with an inner volume, a heat exchanger retained by the cabinet structure, a fan retained by the cabinet structure, a motor operative to drive the fan, a primary air inlet disposed in fluidic communication with the inner volume of the main housing, and a duct section interposed between the heat exchanger and the fan. The duct section of the at least one indoor cassette unit can, for example, comprise a tapered duct section.

In embodiments of the invention, the cabinet structure of the at least one indoor cassette unit comprises the main housing and a secondary housing fixed to the main housing wherein the secondary housing has an inner volume. The duct section of the at least one indoor cassette unit establishes a physically spaced distance and a substantially enclosed sub-volume within the main housing between the refrigerant coil and the fan. Furthermore, the at least one indoor cassette unit can additionally include a return air inlet disposed in fluidic communication with the inner volume of the main housing.

Where the main housing of the indoor cassette unit has a first end portion, a second end portion, and a mid-portion between the first and second end portions, the heat exchanger can, for instance, be retained in the first end portion of the main housing. The primary air inlet can, in embodiments of the system, be retained in the second end portion of the main housing of the indoor cassette unit. The system can additionally include a return air inlet disposed in the main housing of the indoor cassette unit. The return air inlet of the indoor cassette unit can, for example, be disposed in the second end portion of the main housing in parallel with the primary air inlet.

These and further objects and advantages of embodiments of the invention will become obvious not only to one who reviews the present specification and drawings but also to one who has an opportunity to experience a variable refrigerant flow system as disclosed herein in operation. It will be appreciated, however, that, although the accomplishment of each of the foregoing objects in a single embodiment of the invention may be possible and indeed preferred, not all embodiments will seek or need to accomplish each and every potential object and advantage. Nonetheless, all such embodiments should be considered within the scope of the invention.

One will appreciate that the foregoing discussion broadly outlines the more important features of the invention merely to enable a better understanding of the detailed description that follows and to instill a better appreciation of the inventor's contribution to the art. Before an embodiment of the invention is explained in detail, it must be made clear that the following details of construction, descriptions of geometry, and illustrations of inventive concepts are mere examples of the many possible manifestations of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying figures:

FIG. 1 is a schematic view of a variable refrigerant flow system;

FIG. 2 is a schematic top plan view of an indoor cassette unit for a variable refrigerant flow system according to the prior art;

FIG. 3 is a schematic, sectioned plan view of an indoor cassette unit for a variable refrigerant flow system as disclosed herein;

FIG. 4 is a perspective view of an alternative indoor cassette unit according to the invention;

FIG. 5 is a perspective view of a further embodiment of the indoor cassette unit;

FIGS. 6 and 7 are alternative perspective views of still another embodiment of the indoor cassette unit; and

FIG. 8 is a perspective view of a further manifestation of the indoor cassette unit taught herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The variable refrigerant flow system disclosed herein is subject to varied embodiments, each within the scope of the invention. However, to ensure that one skilled in the art will be able to understand and, in appropriate cases, practice the present invention, certain preferred embodiments of the broader invention revealed herein are described below and shown in the accompanying drawing figures.

A variable refrigerant flow or VRF system is indicated generally at 100 in FIG. 1. As set forth hereinabove, the VRF system 100 uses refrigerant as the cooling and heating medium. The refrigerant is conditioned by an outdoor condensing unit 102 and circulated within the building 200 to multiple cassette fan-coil units or FCUs 104A, 104B, 104C, . . . 104 n. The outdoor unit 102 commonly includes one or more compressors 106 operative to release collected heat to the outside air. One or more condensers 108 operate as pumps to move the working fluid. A fan or fans 110 conduct air through the outdoor condensing unit 102 operates, for instance, to circulate air through the outdoor unit 102. The indoor cassette FCUs 104A, 104B, 104C, . . . 104 n typically include an expansion device 112, a blower or fan 114, and a heat exchanger 116, such as a coil heat exchanger 116.

The indoor cassette fan-coil units 104A, 104B, 104C, . . . 104 n act as local air circulation units to circulate the indoor air within plural spaces, such as rooms, hallways, or other spaces 202A, 202B, 202C, . . . 202 n in which the indoor cassette FCUs 104A, 104B, 104C, . . . 104 n are disposed. The coil heat exchangers 116 within the indoor cassette FCUs 104A, 104B, 104C, . . . 104 n are chilled or heated by the fluid, and the heat exchanger 116 adjusts the temperature or humidity of the circulated air while the fan or blower 114 circulates the indoor air. The VRF cassette fan-coil units 104A, 104B, 104C, . . . 104 n, each with a heat exchanger 116 and an air distribution device in the form of the blower or fan 114, are disposed within the occupied zone to deliver conditioned air. In this illustrated example, the indoor cassette FCUs 104A, 104B, 104C, . . . 104 n are mounted within the ceilings 204 of the spaces 202A, 202B, 202C, . . . 202 n with it being understood that indoor cassette FCUs 104A, 104B, 104C, . . . 104 n can alternatively be mounted in relation to walls or other locations in communication with the spaces 202A, 202B, 202C, . . . 202 n to be heated or cooled. Heating and cooling operation of the indoor cassette FCUs 104A, 104B, 104C, . . . 104 n can be individually adjusted, such as by remote control units 128 or hard-wired control units 130.

The VRF system 100 incorporates an inverter 118 that converts incoming alternating current from a power source 206 to direct current. The direct current passes through a frequency driver 120 so that the speed of a variable speed motor 122 can be controlled. Refrigerant lines 124 and 126 establish a refrigerant loop. The variable speed motor 122 enables variable refrigerant flow through the refrigerant lines 124 and 126 rather than simple on/off operation. Variable speed operation of the motor 122 and the consequent variable refrigerant flow permits VRF systems 100 to work only at the rate necessary, which allows for substantial energy savings at partial-load conditions. Further, plural compressors 106 and even plural outdoor units 102 of similar or different capacities can be operated in response to changes in the cooling or heating requirements within the air conditioned spaces 202A, 202B, 202C, . . . 202 n. Heat recovery VRF technology allows individual indoor cassette FCUs 104A, 104B, 104C, . . . 104 n to heat or cool their respective spaces 202A, 202B, 202C, . . . 202 n as required with resultant energy savings and greater control of the building's interior temperature.

As noted previously, while VRF HVAC systems 100 of the prior art offer benefits regarding energy savings and temperature control proximate to the indoor cassette FCUs 104, there are disadvantages in prior art configurations as can be appreciated with further reference to FIG. 2. For instance, indoor cassette FCUs 104 as employed under the prior art are poorly effective at distributing air. It is known, for example, that warm air is best distributed at the perimeter of a space, which is where the heat loss primarily occurs. Distributing warm air from the center of the room 202 or in four different directions as is the case with certain prior art fan-coil cassette units 104 is inefficient. Warm air, if being distributed from the ceiling, should be introduced into the space 202 so that it can be sent vertically downward along the perimeter of the space 202. Moreover, with respect to wall-mounted fan-coil cassette units 104, it is further recognized that cool air distributed from the wall 208 may create drafts in the occupied space 202.

An indoor cassette unit as disclosed herein is indicated generally at 10 in FIG. 3. The indoor cassette unit 10 is operable as an indoor cassette FCU 10 of a variable refrigerant flow HVAC system 100 in replacement of one or more of the indoor cassette FCUs 104A, 104B, 104C shown and described in relation to FIG. 1.

The indoor cassette unit 10 has a main enclosure or housing 12 that defines an inner volume. A heat exchanger 14, such as a refrigerant coil 14 with a condensate drain pan, is retained by the enclosure formed by the main housing 12. The refrigerant coil 14 in this embodiment of the indoor cassette unit 10 is retained at a first end portion of the main housing 12. A tapered duct section 16 has a first end in communication with the refrigerant coil 14 and a second end in communication with a fan 18 with a motor 19, which are disposed in a central portion of the housing 12. The duct section 16 establishes a physically spaced distance and a substantially enclosed sub-volume within the main housing 12 between the refrigerant coil 14 and the fan 18.

A primary air inlet 22, which can include an inlet volume sensing device 23 and a volume control device 25, is disposed at a second end portion of the housing 12. A plenum or return air inlet 20 is likewise disposed to the second end portion of the housing 12 in parallel with the primary air inlet 22. Under this construction, the refrigerant coil 14 is decoupled from and disparately located in relation to the air distribution components. The refrigerant coil 14 is, for instance, retained by the main housing 12 physically spaced from the return air inlet 20 and the primary air inlet 22.

Depending on the embodiment of the indoor cassette unit 10, the plenum or return air inlet 20 could additionally incorporate a filter rack and filter. Where included, the filter rack can be sized to accommodate various sizes and thicknesses of filters. In use, the filter rack and filter will operate to keep the refrigerant coil 14 clean by filtering plenum/return air. Moreover, as previously set forth, a condensate tray can be disposed to collect any condensate dripping from the refrigerant coil 14 when the cassette 10 is in a cooling mode. In each disclosed configuration, the cassette 10 can additionally incorporate ultraviolet lighting to provide UVGI (Ultra Violet Germicidal Irradiation) thereby further helping to keep the refrigerant coil 14 clean.

The indoor cassette unit 10 further incorporates a larger fan 18 with a primary air inlet 22. With the cassette 10 so constructed, air can be distributed in the location and manner that is most efficient while providing occupants with optimal comfort. In practice, one or more ducts 210 can connect the disclosed cassette 10 to conventional air distribution devices. With multiple air distribution devices, better distribution can be achieved.

Employing a larger fan 18 physically spaced from and thus disparately located in relation to the refrigerant coil 14 with the tapered duct section 16 therebetween serves two purposes. First, additional air distribution power is required to overcome the additional pressure due, for example, to added ductwork 210. Second, additional air distribution power allows more air to be brought from the ceiling plenum where the indoor cassette 10 may be installed. The additional air flow reduces the discharge temperature differential, which facilitates adherence to the ASHRAE standard, is more efficient, and provides better comfort.

Where the primary air inlet 22 incorporates or is operative as an air valve, such as through an inlet volume sensing device 23 and a volume control device 25, a controlled amount of additional air can be selectively supplied to the unit. This additional air can supply the amount of fresh air required to meet, for instance, design parameters or local code. In certain practices of the invention, the supplied fresh air could be provided as what may be referred to as cool air thereby reducing the cooling load of the heat exchanger 14 and reducing the latent load the heat exchanger 14 needs to condition. For example, the fresh air could be supplied at or near room temperature to avoid overcooling the space when cooling loads are low.

The supplied volume of fresh air could be monitored and modulated. For example, the air valve, such as that established by the inlet volume sensing device 23 and the volume control device 25, could be shut when there is no human occupancy in the space thus leaving the fan 18 and coil 14 responsible for maintaining temperature.

Furthermore, the disclosed cassette unit 10 enables combination fan, coil, and valve terminals that could be large enough to meet all load requirements of larger zones. One terminal point can thus be used instead of many. With that, the required piping, labor, and controls are reduced. This is in opposition to cassettes of the prior art, which commonly require multiple cassettes within a single zone.

Decoupling the refrigerant coil 14 and the fan 18 by physically spacing the same, such as with, by way of example and not limitation, a duct section 16 or other physically spaced distance and substantially enclosed sub-volume therebetween, also permits variation in the possible relative configurations of the coil 14, the fan 18, and the valve of the primary air inlet 22 formed by the inlet volume sensing device 23 and the volume control device 25. For instance, by having an enclosure 12 that houses or retains all three components, such as with the coil 14 mounted on the plenum air inlet 22, it would be possible to turn off the fan 18 and the coil 14 to have just the supply air valve of the air inlet 22 provide air to the zone. In areas of the world where “free cooling,” also known as economizer cooling, is available, the cassette unit 10 would allow for the coil 14 to be shut down. Depending upon the configuration of the components, the fan 18 could be turned off to provide cool air to meet the required load through the primary air valve of the air inlet 22. One or more indoor cassette units 10 according to the invention can form components of a VRF system formed by an outdoor unit 102 and the indoor cassette units 10.

With indoor cassette units 10 as disclosed herein, the coil heat exchanger 14 can vary in position within the cassette 10. In one other non-limiting example, the refrigerant coil 14 can be located downstream of the fan 18, such as between the fan 18 and the discharge duct 210. Under such constructions, air from the primary system will pass across the coil 14 and can be cooled or heated as the zone requires.

In other embodiments of the indoor cassette unit 10, the refrigerant coil 14 can be positioned between the plenum air inlet 20 and the fan 18. The fan 18 can be installed within the cassette 10 so that primary air can bypass the fan 18 to be supplied to the occupied zone without passing over the coil 14.

Pursuant to the invention, the fan 18 can be powered, by way of example and not limitation, by a permanent split capacitor (PSC) motor 19. In other embodiments, the fan 18 could be powered by an electronically commutated motor (ECM) 19 thereby allowing for variable speeds that can correspond to the call for air flow.

As shown in the drawings, the primary air inlet 22 can be equipped with a device to measure air flow 23. The air flow measurement device 23 could, for example, be a differential pressure measurement system, an electronic measurement system, or any other effective air flow measurement system that may now exist or hereafter be developed.

As is further illustrated, the primary air inlet 22 can additionally incorporate a mechanism for controlling the volume of air passing through the inlet 22. By way of example and not limitation, the volume control device 25 could take the form of a round, oval, square, or rectangular damper 25.

The variable refrigerant flow indoor cassette unit 10 of FIG. 3 can thus be considered to be founded on a cassette enclosure or common cabinet 12, which may alternatively be referred to as a main housing or enclosure. A refrigerant coil 14 with a condensate tray, a fan 18 with a motor 19, and a primary air inlet 22 are installed in or on the common cabinet 12. The air from the return air inlet 20 and the primary air inlet 22 is moved through the cabinet 12 and into the downstream duct 210 by the fan 18 and motor 19.

An alternative configuration of the variable refrigerant flow indoor cassette unit 10 is illustrated in FIG. 4. The indoor cassette unit 10 is founded on a housing 12 that defines a main inner volume. In FIG. 4, the side walls and top of the housing 12 are removed for clarity of understanding. A heat exchanger or refrigerant coil 14 with a condensate tray is retained at a first end of the housing 12. A filter rack 24 can retain one or more filters in a facing relationship with the heat exchanger 14. A primary air inlet 22 is retained at the first end of the housing 12 adjacent to the heat exchanger 14. A tapered duct section 16 has a first end in communication with the refrigerant coil 14 retained at a first end of the housing 12 and a second end in communication with a fan 18, which is disposed within a central portion of the housing 12. The duct section 16 again establishes a physically spaced distance and a substantially enclosed sub-volume within the main housing 12 and between the refrigerant coil 14 and the fan 18. A discharge connection 28 is disposed at a second end of the housing 12. The discharge connection 28 can be connected to downstream ductwork 210.

Primary air can thus be moved through the cabinet 12 during operation of the cassette 10. The air can, in certain practices, be moved by main system pressure and can be independent of the cabinet fan 18 to provide fresh or ventilation air to the occupied zone. When the refrigerant coil 14 is required to provide heating or cooling to the space, the cabinet fan 18 can turn on and induce plenum air across the coil 14 and move the air through downstream ductwork 210 into the occupied zone.

Further configurations of the variable refrigerant flow indoor cassette unit 10 are depicted in FIGS. 6, 7, and 8 with like reference numbers indicating like components. In FIGS. 6 and 7, primary cabinet 12 defines an inner volume and has a first end and a second end. A refrigerant coil 14 is retained at a first end of the primary cabinet 12, and a filter rack 24 can retain one or more filters in juxtaposition with the refrigerant coil 14. A tapered duct section 16 has a first end in communication with the refrigerant coil 14 retained at the first end of the housing 12 and a second end in communication with a fan 18, which is disposed within a central portion of the housing 12. The duct section 16 again establishes a physically spaced distance and a substantially enclosed sub-volume within the main housing 12 and between the refrigerant coil 14 and the fan 18. In the embodiment of FIGS. 6 and 7, the primary air inlet 22 is disposed in a wall of a secondary cabinet 32. The cabinets 12 and 32 are attached and in fluidic communication. There is a common discharge duct connection 28 for the discharge air of both cabinet sections 12 and 32. A back draft or control damper 26 is disposed in juxtaposition with the common discharge duct connection 28, such as between the inner volume of the main housing 12 and the discharge duct connection 28.

The cassette unit 10 of FIG. 8 is similarly constructed to that of FIGS. 6 and 7. However, the refrigerant coil 14 and the juxtaposed filter rack 24 are disposed in a wall of the main cabinet 12 with the primary air inlet 22, which is again retained in a wall of a secondary cabinet 32, aligned in parallel with the orientation of the coil 14 and the wall of the main housing 12 that retains the same. The common discharge duct connection 28 is disposed to span the walls of the main cabinet 12 and the secondary cabinet 32 opposite the refrigerant coil 14 and the primary air inlet 22.

Another embodiment of the variable refrigerant flow indoor cassette unit is shown in FIG. 5 where the cassette is again indicated at 10. There, the cassette 10 again has a primary cabinet 12 and a secondary cabinet 32. The volume of the primary cabinet 12 can, but need not necessarily, be separated from the volume of the secondary cabinet 32 by an internal wall 30. The primary air inlet 22 is disposed in the secondary cabinet 32, and the main cabinet 12 and the secondary cabinet 32 share a common discharge connection 28. A refrigerant coil 14 with a condensate drain pan is retained by the main housing 12, such as at a first end portion thereof. A tapered duct section 16 has a first end in communication with the refrigerant coil 14 and a second end in communication with a motorized fan 18 disposed in a central portion of the main housing 12. A back draft or control damper section 26 is interposed between the duct section 16 and the fan 18. The primary air inlet 22, which again can include an inlet volume sensing device 23 and a volume control device 25, is disposed in communication with the secondary cabinet 32. A filter rack and filter 24 is disposed to overlie the refrigerant coil 14.

The configuration of the indoor cassette unit 10 of FIG. 5 corresponds to that of FIGS. 6 and 7 in that the primary air is moved through a primary air inlet 22 by main system pressure and is not dependent on the fan 18 of the primary cabinet 12 to provide fresh or ventilation air to the occupied zone. When the refrigerant coil 14 is required to provide heating or cooling to the space, the cabinet fan 18 can be actuated to provide energy sufficient to induce plenum air across the coil 14 and move the air through the downstream ductwork into the occupied zone.

The indoor cassette unit 10 disclosed herein and variable refrigerant flow systems 100 incorporating the same are thus operative to couple the ventilation system with the fan 18 and heat exchanger 14 to provide benefits not available with known current offerings and to decouple the fan 18 and heat exchanger coil 14 components from the air distribution system to avoid the inherent problems and issues associated with known current offerings and to facilitate meeting current standards and codes.

Separating the ventilation or ‘fresh air’ and the plenum air in a parallel configuration allows the air to mix after the coil 14 which increases the total air flow and decreases the discharge air in the heating mode. A lower discharge temperature means less stratification and more warm air can get to the occupied zone. More air means a larger mass which means it is easier to drive the air down into the occupied zone if distributed through an appropriate air diffusing device. The series version of the indoor cassette unit 10 with a larger fan 18 allows for more air to be brought across the coil 14, which reduces the discharge temperature of the air in the heating mode. As with the advantages with the parallel configuration, benefits are achieved with lower discharge temperature and larger volume. In each version, the primary air inlet 22 with the inlet volume sensing device 23 and the volume control device 25 permits volume measurement and control. When the space is unoccupied, the valve formed by the volume control device 25 may be closed. The disclosed parallel and series configurations with the primary air inlet 22 with the inlet volume sensing device 23 and the volume control device 25 are capable of delivering additional air when required. The parallel version would allow the coil 14 to be turned off or modulated, and the primary air valve formed by the primary air inlet 22 can be used to supply air in an economizer mode thus providing low energy cooling.

With certain details and embodiments of the present invention for an indoor cassette unit 10 and a variable refrigerant flow system 100 employing one or more such indoor cassette units 10 disclosed, it will be appreciated by one skilled in the art that numerous changes and additions could be made thereto without deviating from the spirit or scope of the invention. This is particularly true when one bears in mind that the presently preferred embodiments merely exemplify the broader invention revealed herein. Accordingly, it will be clear that those with major features of the invention in mind could craft embodiments that incorporate those major features while not incorporating all of the features included in the preferred embodiments.

Therefore, the following claims shall define the scope of protection to be afforded to the inventor. Those claims shall be deemed to include equivalent constructions insofar as they do not depart from the spirit and scope of the invention. It must be further noted that a plurality of the following claims may express, or be interpreted to express, certain elements as means for performing a specific function, at times without the recital of structure or material. As the law demands, any such claims shall be construed to cover not only the corresponding structure and material expressly described in this specification but also all equivalents thereof. 

I claim as deserving the protection of Letters Patent:
 1. An indoor cassette unit for a variable refrigerant flow system, the indoor cassette unit comprising: a cabinet structure comprising a main housing with an inner volume; a heat exchanger retained by the cabinet structure; a fan retained by the cabinet structure; a motor operative to drive the fan; a primary air inlet disposed in fluidic communication with the inner volume of the main housing; and a duct section interposed between the heat exchanger and the fan.
 2. The indoor cassette unit of claim 1 wherein the duct section interposed between the heat exchanger and the fan comprises a tapered duct section.
 3. The indoor cassette unit of claim 1 further comprising an inlet volume sensing device and a volume control device operably associated with the primary air inlet.
 4. The indoor cassette unit of claim 1 wherein the cabinet structure comprises the main housing and a secondary housing fixed to the main housing wherein the secondary housing has an inner volume.
 5. The indoor cassette unit of claim 1 further comprising a filter rack retained by the cabinet structure.
 6. The indoor cassette unit of claim 5 wherein the filter rack is disposed in juxtaposition with the heat exchanger.
 7. The indoor cassette unit of claim 1 wherein the heat exchanger comprises a refrigerant coil.
 8. The indoor cassette unit of claim 1 wherein the duct section establishes a physically spaced distance between the heat exchanger and the fan.
 9. The indoor cassette unit of claim 8 wherein the duct section establishes a substantially enclosed sub-volume within the main housing between the refrigerant coil and the fan.
 10. The indoor cassette unit of claim 1 further comprising a return air inlet disposed in fluidic communication with the inner volume of the main housing.
 11. The indoor cassette unit of claim 1 wherein the main housing has a first end portion, a second end portion, and a mid-portion between the first and second end portions and wherein the heat exchanger is retained in the first end portion of the main housing.
 12. The indoor cassette unit of claim 11 wherein the primary air inlet is retained in the second end portion of the main housing.
 13. The indoor cassette unit of claim 12 further comprising a return air inlet disposed in the main housing.
 14. The indoor cassette unit of claim 13 wherein the return air inlet is disposed in the second end portion of the main housing in parallel with the primary air inlet.
 15. The indoor cassette unit of claim 11 wherein the primary air inlet is retained in the first end portion of the main housing and further comprising a discharge connection disposed in the second end portion of the main housing.
 16. The indoor cassette unit of claim 1 wherein the cabinet structure comprises the main housing and a secondary housing fixed to the main housing, wherein the secondary housing has an inner volume, and wherein the primary air inlet is disposed in the secondary housing.
 17. The indoor cassette unit of claim further comprising a discharge connection in fluidic communication with the main housing and the secondary housing.
 18. A variable refrigerant flow system comprising: an outdoor condensing unit comprising at least one compressor, at least one condenser, a fan, and a variable speed motor; an inverter operative to convert incoming alternating current to direct current supplied to the variable speed motor of the outdoor condensing unit; at least one indoor cassette unit; refrigerant lines that fluidically connect the outdoor condensing unit and the at least one indoor cassette unit to establish a refrigerant loop; wherein the at least one indoor cassette unit comprises a cabinet structure comprising a main housing with an inner volume, a heat exchanger retained by the cabinet structure, a fan retained by the cabinet structure, a motor operative to drive the fan, a primary air inlet disposed in fluidic communication with the inner volume of the main housing, and a duct section interposed between the heat exchanger and the fan.
 19. The variable refrigerant flow system of claim 18 wherein the duct section of the at least one indoor cassette unit comprises a tapered duct section.
 20. The variable refrigerant flow system of claim 18 wherein the cabinet structure of the at least one indoor cassette unit comprises the main housing and a secondary housing fixed to the main housing wherein the secondary housing has an inner volume.
 21. The variable refrigerant flow system of claim 20 wherein the duct section of the at least one indoor cassette unit establishes a physically spaced distance and a substantially enclosed sub-volume within the main housing between the refrigerant coil and the fan.
 22. The variable refrigerant flow system of claim 18 wherein the at least one indoor cassette unit further comprises a return air inlet disposed in fluidic communication with the inner volume of the main housing.
 23. The variable refrigerant flow system of claim 18 wherein the main housing of the indoor cassette unit has a first end portion, a second end portion, and a mid-portion between the first and second end portions and wherein the heat exchanger is retained in the first end portion of the main housing.
 24. The variable refrigerant flow system of claim 23 wherein the primary air inlet is retained in the second end portion of the main housing of the indoor cassette unit.
 25. The variable refrigerant flow system of claim 24 further comprising a return air inlet disposed in the main housing of the indoor cassette unit.
 26. The variable refrigerant flow system of claim 25 wherein the return air inlet of the indoor cassette unit is disposed in the second end portion of the main housing in parallel with the primary air inlet. 